BASIC COMPONENTS OF AN EARTH DAM

An earth dam consists of three basic components, i.e.

1. Foundation
2. Core or (membrane)
3. Shell
4. Transition Filter
5. Internal Drain
6. Toe Drain

1. Foundation

It consists of either earth or rock and provides a support for the embankment and resists both vertical and horizontal loads. It also resists under seepage on the flow of water beneath the dam.

2. Core or Membrane

It holds back the free water of the dam reservoir. It is located either at the centre or upstream from the centre of the dam. In case of rock fill dams, the core is provided on the upstream face. To resist the under seepage, the core is extended down into the foundation till an impervious layer of sufficient thickness is reached. The extension of the core into the foundation is termed as a cut off.

3. Shell

It provides structural support for the core and distributes the load over the foundation. The dams which are constructed of the same materials are called homogeneous dams. Small dams can suitably be constructed as homogeneous dams if the available materials are suitable.

4. Transition Filter

In core dams, a transition filter between the core and shell is generally provided to prevent the migration of the fine grained core materials into the pores of the coarse grained shell materials. In case of difference in particle sizes of the materials of the core and shell is small, the transition filter is omitted but in case of clay cover and rock or gravel shell, a transition filter is necessarily provided.

5. Internal Drain

An internal drain is provided on the downstream side of the dam to carry away the seepage through the core and cut off, and also to prevent the saturation of the upper part of the downstream shell by rain on the dam.

6. Toe Drain

A toe drain is provided at the downstream face of the shell. A riprap or grating is provided to cover the upstream face to prevent erosion or wash by waves.